Tech Topic: OSB vs. Plywood Decking
OSB and plywood are two common wood deck types used in new construction projects across our industry. While they may appear similar, each offers different levels of performance and withdrawal resistance.
OSB decks are not included in Carlisle’s list of approved deck types. However, they are acceptable on warranted projects provided the fastening rate increases to ensure proper membrane and insulation securement. Carlisle’s Specification and Detail Manual outlines the minimum fastening requirements based on the use of one of the four approved deck types:
Minimum 15/32" 3-ply plywood
Minimum 1-1/2" wood plank
22-gauge (or heavier) steel
Structural concrete
When OSB is specified, enhanced fastening is necessary to meet performance standards.
OSB, gypsum, Tectum, lightweight structural concrete, and steel decks less than 22 gauge all require increased fastening rates for adhered systems—typically a minimum of 16 plates and fasteners per board. This number may increase further based on building height, warranty duration, wind speed, and other project-specific variables.
OSB can significantly impact the number of plates and fasteners required on an adhered project due to the projected pull-out values with that deck type. The total amount of plates and fasteners required can be quite drastic on an OSB when compared to the insulation/underlayment attachment requirements for the same warranty and system on one of the approved deck types.
You can also find the membrane securement enhancement requirements for OSB decks in mechanically fastened systems. Carlisle requires a minimum of two perimeter sheets when the membrane is secured to an OSB deck on mechanically fastened projects, regardless of the warranty. Mechanically fastened systems over OSB decks are also limited to a maximum 20-year / 80 MPH warranty, which cannot be exceeded.
OSB is still an acceptable deck type for warranted projects; however, it’s crucial to understand the differences between OSB and plywood, as each can impact underlayment attachment requirements and membrane fastening criteria. Improperly specifying the deck type during project submission can lead to costly changes and increase the risk of potential leaks—especially if additional securement is required after the project has been completed. Please don’t hesitate to reach out if you have any questions or would like to discuss this topic further.